Not Applicable.
1. Field of the Invention
This invention relates to friction gearing continuously variable transmissions, specifically to an improved mechanism for transmitting power through tractional or frictional engagement of rings, wheels and a disk or disks.
Unique features relate to efficiency, control of loads in response to transmitted torque, control of speed ratio, maximum power capacity, reliability and manufacturing costs.
2. Description of Prior Art
Many continuously variable transmission concepts have been proposed in the past for vehicle and industrial applications.
Electrical, hydraulic, and mechanical methods have been proposed with many sub-categories and many combinations of sub-categories.
No proposed method has yet been accepted in the manner of either manual or automatic transmissions. This is because the prior art has failed in one or more requirements. Poor efficiency has been a major deterrent to most proposed systems. Damage during use or lack of reliability has likewise been a major deterrent. Complexity of control has been a major difficulty. The inability to transmit the power developed by large engines has been a limitation. High precision and high costs of precision have been substantial problems. The need for high capacity bearings to support high contact forces has been a limitation both because of bearing capacity and because of bearing power losses. Bearing power losses are higher with friction enhancing lubricants. Many other miscellaneous problems were also encountered.
Still, it is recognized that a continuously variable transmission which could overcome these problems would have operating fuel economies of real significance because engines, or prime movers, would be able to operate at more economical conditions. Thus saving valuable energy. Simultaneously, a proper continuously variable transmission would produce better acceleration, speed and deceleration performances.
Much of the mechanical prior-art has utilized the principle of transmitting power through rolling contact between two bodies. This principle can be used in a dry atmosphere like air and like halocarbon vapor; or, it can be used in the presence of various liquids. Some liquids have been developed specifically for this purpose and are known as tractants. These tractants lubricate surfaces, as do common oils, but they excel at supporting high shear stresses under contact conditions of high local pressures.
In order to avoid high power losses in traction mechanisms, it is necessary to reduce the contact force when the transmission is operating at less than maximum torque.
On the other hand, a time delay between a sudden increase in torque and the corresponding increase in contact force has been the cause of catastrophic damage to the rolling surfaces when slippage has occurred. Prior-art systems have been too slow to prevent such damage in the worst conditions.
The limited speed range of most of the prior-art has been partially overcome by using various combinations of fixed ratio gearing, clutches, brakes and the like. Compatibility with these systems is not shared by all prior-art but it is a major factor in some systems.
Currently there are three systems which appear to be favored by the automotive industry.
Firstly, the double toric system which has been under development for nearly a century. This system eliminates the need for high capacity bearings to support contact forces, but it suffers from a number of other factors: a. the need to control six rollers all in different planes, simultaneously, in order to change ratio; b. high inertia and flexibility of parts needed to respond to sudden torque changes for the prevention of catastrophic slippage; c. high manufacturing costs for the high precision rollers, concave faces and control mechanisms; d. power losses in the rolling contacts due to what is referred to as xe2x80x9cspinxe2x80x9d.
Secondly, the system known as the double half-toroid. This system minimizes the power losses due to spin but it suffers from: a. the need to support high contact forces with bearings, and their attendant power losses; b. high manufacturing costs for rollers, concave discs, and the control mechanisms; c. the need to control four rollers, in different planes, simultaneously, to change the ratio; d. high inertia of parts needed to respond to a sudden change in torque for the prevention of catastrophic slippage.
Thirdly, the system known as the VanDoorne metal belt. This system has had some success in vehicles with small engines but it suffers from a number of factors: a. it can""t handle the power from big engines; b. it has poor efficiency when operarted at part load; c. the ratio change hydraulics have to be coordinated with the pressure needed to prevent slippage; d. the system is noisy.
In short, the prior-art has to be improved substantially to meet the requirements of a successful system. Such improvements are described in the following explanation of the invention.
It is an object of the present invention to provide a continuously variable transmission system of high efficiency.
It is another object of the invention to provide a continuously variable transmission with improved resistance to slipping damage encountered by sudden changes in torque.
It is yet another object of the invention to provide a continuously variable transmission capable of handling the power from large engines as well as from small engines.
Another object is to improve the ease of controlling speed ratio by reducing the complexity of elements needed to effect ratio changes.
It is a further advantage to achieve the above objects in an economical manner using easily manufactured parts.
It is an additional advantage to achieve compatibility with other mechanical devices for extending the speed ratio range.
It is a significant object to provide a continuously variable transmission which is compatible with known oils or tractants.
It is an advantage to eliminate the need for bearings to support high contact forces because of their cost, because of their power losses and because of their size limitations.
These and other objects and advantages of the present invention will become apparent from the following description of the accompanying drawings, which disclose several embodiments of the invention. It is to be understood that the drawings are to be used for purposes of illustration only, and not as a definition of the invention.
In accordance with the present invention, a disk is interposed between members of two friction gearing planetaries so as to permit transmission input and output speed ratios to be changed by changing the position of the disk with respect to the planetaries, simultaneously the contact forces are adjusted to accomodate changes in torque.